Generally, various properties are imparted to an eyeglass lens by forming various functional films on the lens substrate while achieving a desired refractive index by means of the lens substrate. Antireflective films imparting an antireflective property to the surface of a lens are widely employed as such functional films. Among them, vapor-deposited films that are formed using a vapor deposition source in the form of ZrO2 are considered advantageous in terms of cost because they are inexpensive among the high refractive index layers constituting a multilayered antireflective film (for example, sec Japanese Unexamined Patent Publication (KOKAI) No. 2009-493022, which is expressly incorporated herein by reference in its entirety).
Eyeglass lenses are required to have good durability without deterioration even when placed in a variety of environments. For example, eyeglass lenses are sometimes worn in the bath, left in the car in summer, and worn by wearers who are active for long periods outdoors. It is desirable for them to maintain good quality without developing cracks when subjected to high temperatures in this manner. However, eyeglass lenses having vapor-deposited films formed the vapor deposition of a vapor deposition source the main component of which is ZrO2 (also referred to hereinafter as “ZrO2 vapor-deposited films” sometimes exhibit a decrease in adhesion between the layers constituting the multilayered antireflective film and a decrease in optical characteristics caused by the development of cracks in the vapor-deposited film at high temperatures.
In the field of manufacturing eyeglass lenses, to stably provide an eyeglass lens the quality of which does not decrease over time, accelerated durability testing is conducted on test samples prepared under candidate manufacturing conditions before determining the manufacturing conditions for actual manufacturing. Manufacturing conditions identical to the manufacturing conditions of those test samples exhibiting good test results arc normally employed in actual manufacturing. For example, when a ZrO2 vapor-deposited film is formed in actual manufacturing under the manufacturing condition yielding test samples with little crack generation in accelerated durability testing by heating in an oven, it is possible to obtain an eyeglass lens exhibiting good durability without deterioration of the vapor-deposited film over an extended period of actual use.
Although the above accelerated durability testing has become essential and indispensable for reliably providing an eyeglass lens exhibiting good durability over an extended period, in the present circumstances, to manufacture an eyeglass lens that will pass the accelerated durability testing, candidate vapor deposition conditions are determined for manufacturing a finished product eyeglass lens, a ZrO2 vapor-deposited film is formed under the vapor deposition condition that has been determined to prepare an eyeglass lens, and the eyeglass lens that has been prepared is subjected to accelerated durability testing. When the evaluation standards are not met, new candidate vapor deposition conditions must be selected and the whole series of steps repeated once again in a process of trial and error.